The present invention relates to valves, and in particular it relates to a valve for the control of large-section flows, in particular for compressors or the like.
In compressors the control of flows having large diameters, between 40 and 400 mm, is combined with opening/closing frequencies which can be very high, for instance thousands of cycles per minute. These particular needs have brought to the evolution towards automatic valves, i.e. in which the closure device is forced in the closing position of the aperture by suitably designed elastic return means, said valves being formed so that the moving equipment can rapidly react, therefore by dividing the aperture into a plurality of orifices with parallel axes or coaxial one with respect to the other.
The problems resulting from this kind of approach are connected to the high number of stresses exerted onto moving portions, considering that in a compressor operating at 1,000 rpm a closure device is subject to 1,000 opening shocks and 1,000 closing shocks, besides the effort exerted onto the springs. As far as the latter are concerned, it should be observed that their design is difficult in order to obtain a homogenous load distribution in the valve seat. Another disadvantage to overcome concerns losses of head undergone by the fluid while going through the valve channels.
Moreover, a great attention is directed to the possibility of reducing the flow rate according to the request of compressed fluid, so as to save power. Generally, the reduction of flow rate corresponds to a delay in closing intake valves, which results in a reduction of the effective volume of the fluid to be compressed. At present said reduction is obtained by means of linear actuators acting onto the automatic valves and pneumatically driven. In some cases complex electro-hydraulic controllers are used: an example of this kind is disclosed in EP-A-0893605.
U.S. Pat. No. 5,695,325 discloses another system used to obtain a reduction of flow rate in fluid compressors; in this case the aim is reached by a reciprocal rotation between valves and their seats, so as to prevent their closure for a given period of time calculated on the basis of the amount of flow rate to be reduced.
In order to overcome problems concerning wear and control of automatic valves, rotating valves equipped with driving means have been carried out. EP-A-0971160 describes an actively driven valve for a piston compressor with a valve plate and a counter-plate, both equipped with passage apertures; the valve plate is supported so as to turn around the longitudinal axis of the valve and with respect to the counter-plate. Moreover, it is provided for a driving device firmly connected to the valve plate so as to rotate it with respect to the counter-plate. Problems concerning frictions and sealing between plate and counter-plate, and also those concerning the retrieval of clearances due to wear are solved by using a combined translation-rotation motion of the plate with respect to the counter-plate, said translation being driven along the rotation axis of said counter-plate.
A problem arising from this kind of choice concerns the reciprocal sealing between plate and counter-plate and the efforts undergone by the means translating the plate towards the counter-plate.
The aim of the present invention, therefore, is to provide a valve which best suits the needs of apparatus such as fluid compressors, minimizing problems concerning operating frequency and losses of head while going through valve channels, and which also enables a simple control of the compressor flow rate without using complex and expensive integrating systems.
The scope of the present invention, therefore, is a valve for the control of large-section flows with high operating frequency, and in particular for compressors or the like, comprising a flow aperture and a closure device, said flow aperture comprising one or more orifices formed on a fixed body cooperating with said closure device and introduced into the flow channel, said closure device being rotatable with respect to an axis perpendicular to the body on which said flow aperture lies, and provided with driving means, characterized in that said closure device is equipped with at least a hollow on its surface facing said fixed body housing an insert, said insert being formed so as to be substantially complementary with said orifice of said fixed body.
In a preferred embodiment, said closure device is mounted for rotation about a shaft coupled at one end with driving means and rotatably and sealingly mounted into said fixed body. Advantageously, said closure device is mounted on the side of the fixed body corresponding to flow direction in the valve.